A394240 Number of regions formed by extending the faces of a regular n-gonal pyramid.

15, 23, 38, 51, 73, 91, 120, 143, 179, 207, 250, 283, 333, 371, 428, 471, 535, 583, 654, 707, 785, 843, 928, 991, 1083, 1151, 1250, 1323, 1429, 1507, 1620, 1703, 1823, 1911, 2038, 2131, 2265, 2363, 2504, 2607, 2755, 2863, 3018, 3131, 3293, 3411, 3580, 3703, 3879

Offset

3,1

Links

Paolo Xausa, Table of n, a(n) for n = 3..10000

Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).

Formula

a(n) = (3*n^2-n+6)/2, n odd, and a(n) = (3*n^2-2*n+6)/2, n even.

Mathematica

LinearRecurrence[{1, 2, -2, -1, 1}, {15, 23, 38, 51, 73}, 50] (* Paolo Xausa, Jun 22 2026 *)

Crossrefs

Cf. A249333.

Sequence in context: A129387 A341170 A171167 * A242412 A364729 A195036

Adjacent sequences: A394237 A394238 A394239 * A394241 A394242 A394243

Keyword

nonn,easy

Author

Zinuo Cheng, Jun 15 2026

Status

approved